Fig. 1

MRI of a 3-year-old boy with seizures and delayed motor and mental development. a, b Sagittal and parasagittal T1-weighted images of the brain show cystic dilatation of the fourth ventricle which extends posteriorly filling out nearly the entire posterior fossa, and cerebellar hypoplasia mainly involving the vermis. Elevation of tentorium and torcula with mild hydrocephalic changes. c, d FLAIR and axial T2-weighted image shows the molar tooth sign with elongated, thickened, and horizontally orientated superior cerebellar peduncles (arrows) and a deepened interpeduncular fossa. Final diagnosis: DWM with Joubert syndrome